Study On Hydrodynamic Characteristics And Mass Transfer Process In A Novel Pulsed Extraction Column

Solvent extraction is a common unit operation and has been widely used in separation fields of chemical engineering,the development of high-performance extraction equipment has become the focus of current research.In order to improve the two-phase flow pattern and enhance the efficiency of extraction column,a conical cross-flow tray with no downcomer and independent passages for two-phase fluid is designed.However,when this tray is applied to dealing with high interfacial tension systems,there are some problems,such as large diameter of dispersed phase droplets,the droplets are difficult through the sieve pore and easily gathered under the tray.Therefore,in order to broaden the application ranges and increase the processing capacity of this tray,it is installed in a pulsed extraction column with an inner diameter of 75 mm,based on and the hydrodynamic characteristics and mass transfer process,the separation performance of this extraction column is studied.The main conclusions are as follows:Hydrodynamic characteristics of extraction column are investigated in the system of kerosene-water and 10%tributyl phosphate in kerosene-water without mass transfer.It is showed that when the pulsed intensity increases,the flow characteristics in the column are greatly changed,and the operation areas such as mixer-settler regime and dispersion regime appear successively.In the dispersion regime,the hold-up increased with the increase of pulsed intensity,the droplets dispersed uniformly and its diameter decreased significantly compared with no pulse,it shows good two-phase flow characteristics and is more beneficial to the operation of extraction column.In addition,the critical pulsed intensity(Af)t between the mixer-settler regime and dispersion regime of this column is lower than that of pulsed sieve-plate column,and smaller pulsed intensity is required to reach the dispersion regime.Finally,within certain range,the liquid flooding capacity is less affected by pulsed intensity,and the extraction column has better operation flexibility and stability,this tray can be applied to the pulsed extraction field,but it more suitable for the separation of higher interfacial tension systems contrast with lower interfacial tension systems.Mass transfer performance of extraction column are measured with kerosene-water system and benzoic acid as the solute.Conclusion showed that the addition of pulse significantly increased the separation efficiency,but also increased the effects of axial mixing on the extraction column,the ratio between the height of dispersion mass transfer unit HocD and height of true mass transfer unit Hoc is up to 20%.In addition,the total volume mass transfer coefficient increases with the increase of the dispersed phase velocity,while the continuous phase velocity has little effect,which is consistent with the hydrodynamic experimental results.Finally,the mathematical model of extraction column is established and solved,which shows that axial diffusion model is suitable for the prediction of mass transfer process in extraction column.Based on the analysis and discussion of the experimental results,empirical correlations of each parameter are proposed by dimensionless analysis method within the experimental range.A good agreement between the experimental values and calculated values from empirical correlation is proved,and the maximum relative errors are all within 20%,which can be used as the data basis and calculations for the design and scale-up of this pulsed extraction column.